Fill level measuring devices are used in a multitude of branches of industry, e.g. in the processing industry, in the chemicals industry and in the foods industry.
A frequently selected type of fill-level measurement is based on the travel-time principle. In such case, e.g. periodically short send-signals, e.g. microwaves or ultrasonic waves, are transmitted to the upper surface of a fill substance, and the echo-signals reflected from the upper surface received back, following a distance-dependent travel time, or time-of-flight. An echo function representing echo amplitude as a function of travel time is formed. Each value of this echo function corresponds to the amplitude of an echo reflected at a certain distance from the antenna.
From the echo function, a wanted echo is determined, which probably corresponds to the reflection of a signal sent to the upper surface of the fill substance. In such case, it is, as a rule, assumed that the wanted echo has a greater amplitude than the remaining echoes. From the travel time of the wanted echo one directly obtains, for a fixed propagation velocity of the transmitted pulse, the distance between the fill substance upper surface and the antenna.
Usually, it is not the received, raw signal which is evaluated, but, instead, its so-called envelope, or hull, curve. The envelope curve is produced by rectifying and filtering the raw signal. For accurate determination of a travel time of the wanted echo, first a maximum of the envelope curve is found.
In order that the wanted echo can be recognized and the associated fill level can be derived therefrom, the fill-level measuring device needs certain information. In determining the fill level, e.g. an installation height of the fill-level measuring device in the container must be considered. If not only the separation between fill-level measuring device and fill substance is to be determined, but, also, a figure for the amount of fill substance present in the container, then the fill-level measuring device must also have access to information concerning the shape of the container.
Besides this information, also data concerning material properties of the fill substance can be important. For example, in the case of fill-level measurement by means of microwaves, such a material property is a dielectric constant of the fill substance. How well the fill substance reflects microwaves, i.e. what fraction of the microwaves is reflected, depends on the dielectric constant of the fill substance. Correspondingly, an estimate of the amplitude to be expected for the wanted echo can be made on the basis of the dielectric constant, a procedure which eases the finding of the correct, wanted echo.
Consequently, in the case of conventional fill-level measuring devices, following installation of the fill-level measuring device, a commissioning is done, in which, among other things, all parameters relevant for the particular application are made available to the fill-level measuring device. The parameters are stored as a parameter set and are ready for use, following the commissioning.
After commissioning, the fill-level measuring device then works independently on the basis of the parameter set.
However, it is not that simple to change the application. Each change that affects a parameter of the parameter set requires a newed commissioning. This can involve considerable time and money.